Resistor and method of making the same



Nov. 23, 1948. G. G. HERRICK ETAL RESISTOR AND METHOD. 0F MAKING THESAME l Filed DBG. 13, 1940 y /ZJ Patented Nov. 23,l 1948 BESISTOR ANDMETHOD OF MAKING THE SAME Y George G. Herrick, Benzinger Township, Elk

County, and Hugh N. Veley, St. Marys, Pa., assignors to Speer ResistorCorporation, St.

m Marys, Pa.. a corporation of Pennsylvania Application December 1s,1940, serien No. atomo (ci. coi-c3) .2 Claims.

This invention relates to resistors and methods of making the same, andhas particular reference to the type of molded resistor commonly used inradio apparatus.

This application is, in part, a continuation of our application SerialNo. 307,555, filed December 5, 1939, now Patent No. 2,282,328.

Resistors of the type described above generally comprise conductiveportions formed of powdered carbon, clay, asbestos and other materialsmixed with a binder, such as a phenolformaldehyde resin, pitch or othersimilar material. Generally, though not always, these reslstors areprovided with an insulating shell formed generally of a type of materialsimilar to that of the conductive portion of the resistor, but lackingconductive constituents such as powdered carbon or metal, or the like.It has been the practice in the past to mold first the resistance Aunitand bake it at. the desired temperaturef to set the binder or otherwisefirmly join the ingredients together. Thereafter a coating of aninsulating material was molded under heat and pressure around theresistance unit to provide it with a hard shell.

The present invention contemplates the formation of resistors of thisgeneral type in a series of operations embodying only a single heatingor baking step. In particular, the process contemplates partiallyforming an insulating shell in a suiliciently compacted fashion to causeit to maintain its shape, filling this shell with the conductingmaterial, compressing the two together with the insertion of leads andfinally baking this assembly as a unit. As a result of this operation,the insulating shell andresistance material have more intimate contactwhereby the radiation of heat from the finished resistor is greatlyfacilitated. Thus, for-a given factor of safety, the resistors may bemade of smaller size than those of the prior art, or, if of the samesize, the factor of safety is considerably increased to enable it totake care of substantial overloads.

The invention further contemplates an improved method of incorporatingleads into the resistor to secure products of more uniform resistivity.Resistors of the general type herein referred to have resistancesgenerally diilering quite considerably from their nominal resistances.This is due not only to non-uniformity in the composition of theresistance material, but quite largely due to the varying depth ofpenetration into the resistance material of the end leads. Theseresistors are generally of vquite short length, and slight errors inthis penetration of the leads will give rise to quite substantialpercentage deviations of the actual resistances fro the nominal ones.

A further object of the present invention relates to the location in theresistor of the end leads in such fashion as to secure substantiallybetter uniformity of penetration of the leads into the resistancematerial. Specifically, this is accomplished by providing the leads withuniform hooked ends, or bent ends provided with shoulders, which, in theassembly operation, accurately determine the penetration of the leadinto the resistance material. This advantage of the invention isapplicable to resistors which do not have insulating shells -as well asthose which do.

A further object of the invention relates to the insulation of the endsof the resistor. This is sometimes, though not always, desirable.

These and other objects of the invention. particularly relating todetails, will become apparent from the following description, read inconjunction with the accompanying drawing, in which:

Figures l to 5, inclusive, are diagrammatic sectional views illustratingthe steps leading to the formation of a partially finished insulatingshell;

Figures 6 and 7 are similar views illustrating the assembly of theresistance material, end insulating material and the leads with thispartially formed shelled, and the completion of the molding of theresistor;

Figure 8 is a fragmentary sectional view showing to an enlarged scalethe nature of the finished resistor;

Figure 9 is a fragmentary view similar to Figure 8 showing a modied formof the improved resistor; and

Figure 10 is a further fragmentary view similar to Figure 8 showingstill another form of the improved resistor.

While variations from the preferred method of formation of a resistorwill be obvious, a preferred procedure for the formation of a resistorprovided with an insulating shell will now b e described. A large numberof insulators are simultaneously formed in a press by the duplication ofvarious operating parts, but the drawing is confined to the partscooperating for the formation of a single resistor.

A die plate 2 is provided with a large number of cylindrical openingssuch as 4, each of which serves for the formation and assembly of theparts of a single resistor. Beneath the die 2 are plates 6 and I8carrying respectively compacting sleeves il land pins i2 aligned in apress with the openings il in the die plate 2. The spacings of thesevarious elements, as Well as others which are later described, aremaintained and limited most conveniently by spacing blocks which areplaced between them and removed at various stages of the operation bythe press operator. Initially, the parts just described are located inthe relative positions illustrated in Figure l, with each of the sleeves8 slightly projecting into the corresponding die plate opening [i andwith the top of each pin I2 substantially level with the top of itssleeve, which it closely fits. The operator now pours over the die platethe powdered material A to form the insulating shell, and this is causedto ll up the openings 4, after which the excess may be brushed oif.

There is then placed over the die plate 2 a plate I4 provided withopenings I6 of the same size as. and in alignment with, the openings Il.The plate I is then raised to cause its pins I2 to move upwardly to theposition illustrated in Figure 2 with the result that the powder A isconfined in the annular space between the pin I2 and the walls of theopenings 4 and I6. The openings I6 in this case serve to receive thepowder which is displaced from the openings 4 by the pin I2.

There are now pressed downwardly from above sleeves I8 carried by aplate, not shown. These sleeves serve to compress the insulatingmaterial. This compression is carried out at least to an extent to bringthe compressed shell flush with the upper end of the die 2, asillustrated. though the compression may well be carried out to bring theupper end of the shell below the upper surface of the die. Followingthis operationl and as illustrated in Figure 4, the plate 6 is furtherraised to provide additional compression of the insulating sleeve by thesleeves 8.

The insulating material will now be compressed to a sufilcient extent tocause it to be self-sustaining. Accordingly, the pin I 2 is withdrawnand then the sleeves 8 and I8 are withdrawn and the plate I4 removed.The result is to leave in the openings Il in the die 2 the compactedinsulating shells illustrated in Figure at A'.

A series of lower plungers carried by a plate (not illustrated) areprovided with central openings in which are located 'terminal wires Bprovided with uniform hooked ends C, the free ends of which rest on thetops of the plungers 2li. The die block 2 is assembled with theseplungers so that the plungers are in contact with the bottoms of theshells A.

Into the openings in the shells there is then dusted from the surface ofthe block a small quantity of insulating powder, which maybe of the samecomposition as the insulating shell. This powder forms a layer on thetop of each lower plunger within its shell. Each of the insulatingsleeves A is then filled with the conducting powder E, this powder beingpreferably filled in fiush with the top of the sleeve, whereby itsquantity is quite accurately determined.l Over it is then dusted afurther small amount of insulating powder F, as illustrated.

A second series of plungers 22, similar to 2li, are carried by a plate(not illustrated) and are provided with eentral holes in which arelocated lead wires G similar to the lead wires B and provided withuniform hooked ends, indicated at H, the free ends of which abut thebottoms of the plungers 22. These plungers are then assembled with thelower plungers and dies, desirably while they 4 are in a slopingposition so that the lead wires do not fall out of the upper openings,and the assembly then placed in a press in which pressure is applied toforce both plungers into the openings d, as illustrated in Figure 7. Asa result of this operation, the insulating shell is further compressedto its final length and the conducting material is compressed within it.By reason of this simultaneous compression, the two materials are forcedinto very intimate contact with each other, with the result that in thennal product heat transfer and dissipation is promoted. During thiscompression operation, furthermore, the insulating material D and F iscompressed to seal the ends of the conductive material. During thecompressing operation, the positions of the hooked ends of the leads aredefined by the plunger surfaces whlch abut the free ends of the hooks.Accordingly, they extend accurately predetermined distances into theconductive material.

Following this compression, one of the sets of plungers is withdrawn andthe other forced further inwardly to eject the resistors. These are thenbaked in conventional fashion.

One end of the finished resistor is illustrated in Figure 8, wherein itis shown as comprising the shell A", the resistance element E" bonded tothe shell, the end resistance coating F" and the lead G having itshooked end H flush with the end of the resistor. The end insulation F"may, of course, be omitted if there is no objection to having the endsof the resistance material exposed.

It will be evident that the described procedure results in the formationof a resistor in a simple fashion with the attainment of uniform resultsto the end that the variations of resistance from the nominal resistancevalue may be kept quite low. Thus in cases in use where relativelyslight variations may be critical, this molded type of resistor may beused rather than necessitating recourse to the more accurate and farmore expensive wire wound types. An obvious variation of the proceduremay be adopted if the resistor is to be of the type not having aninsulating shell. We do not claim as new the use of a shoulder duringthe molding to limit the penetration of end leads (this beingillustrated in Nickle Patent 1,847,888, dated March 1, 1932), but merelythe accomplishment of this end by the bending of thin wire leads.

The result of accurate predetermined penetration of the leads into theresistance material may be secured otherwise than by the use of a hookedend on the wire as heretofore described. Instead, a bend may be providedin the lead wire so that when it is received in an opening in acompressing plunger a predetermined length and shape of wire willproject to be embedded in the resistance material. Figure 9 illustratesthis product. The insulator is illustrated as comprising an insulatingshell J sur'ounding the resistance material K. The lead wire L has ahook or otherwire shaped portion M within the resistance material. Theportion M joins the wire at a well defined bend N, which in the processof manufacture, Yessentially the same as that previously described,determines the extent to which the lead wire Amay enter the plungerhole. Thus a predetermined portion of wire of definite shape is embeddedin the resistance material. This lead wire arrangement is also adaptedfor resistors of the uninsulated type but it is not quite assatisfactory for this type as the form previously described because arelatively thin wall will exist outside the bend of the portion M.

The modification illustrated in Figure 10 is a variant of that of Figure8, which is found to improve the strength of insulators of small size.In this case, the shank O is provided with a bent end P embedded in theresistance material. The arrangement diiers from that of Figure 8 inthat the end is slightly deflected to bring'the bend in line with theaxis of the shank, thus causing the bend to lie in a more centralposition in the resistor. As in the case of the modification of Figure8, the free end Q of the bend determines, during the molding process,the extent of penetration of the lead wire into the body.

What we claim and desire to ter:J Patent is:

l. The method of making a molded resistor comprising compressing, in anopening in a die protect by Letand about a pin extending centrallythrough said Vopening, loose insulating material to form a cylinderthereof, withdrawing the pin while leaving the cylinder in said opening,closing the lower end of the cylinder by means of pressure applyingmember carrying a projecting lead wire, lling into the cylinder andabout a projecting portion of the lead wire loose resistance material,and applying to both the cylinder and contained resistance materialpressure by means of said member and a second opposing member alsocarrying a projecting lead wire, thereby to form a resistor having thelead wires embedded in the resistance material thereof. Y

2. 'I'he method of making a molded resistor comprising compressing, inan opening in a die and about a pin extending centrally through saidopening, loose insulating material to form a cylinder thereof,withdrawing the pin while leaving the cylinder in said opening, closingthe lower end of the cylinder by means of a pressure applying membercarrying a projecting lead Wire, filling into the cylinder, insuccession, a small quantity of loose insulating material, a charge ofloose resistance material, and a further small quantity of looseinsulating material, and applying to both the cylinder and containedmaterials pressure by means of a said member and a second opposingmember also carrying a projecting lead wire, thereby to form a resistorhaving insulated ends and having the lead wires embedded in theresistance material thereof.

GEORGE G. HERRICK. HUGH N. VELEY.

REFERENCES CITED The following references are of record in the

